It is one of the most high-profile events for the global Church and would represent the first papal visit to Ireland in 40 years.

The news prompted Assembly member Pat Ramsey to call for Francis to visit Northern Ireland when he visits Dublin in three years' time. Armagh, the ecclesiastical capital of Ireland, could be a destination.

"I welcome this news that the Pope is expected to come to Ireland in 2018. It is absolutely magnificent news for people of all faiths," he said.

"He is filled with so much passion and compassion. He is a highly-regarded Church leader in these modern times and he has enthused and motivated so many people in the Church.

"I would be absolutely delighted for everybody if he could come up north during this visit."

The Pope made the announcement at the conclusion of an outdoor Mass for one million people attending the World Meeting of Families in Philadelphia last night, where Derry soprano Margaret Keys was due to sing for Francis.

Earlier, the Pontiff met Archbishop of Dublin Diarmuid Martin, who will oversee the event in Ireland.

Archbishop Martin said: "The family in Ireland is strong and the Church is called to take up the challenge of ensuring that future Catholic generations are prepared to live their marriage as an itinerary of faith."

The first and only papal visit to Ireland took place in 1979, when Pope John Paul II visited Dublin, Knock, Limerick, Drogheda and Galway.

However, official confirmation of a visit to Ireland by Pope Francis may be some time, due to his age. However, the leader of Ireland's Catholics, Derry-born Archbishop Eamon Martin, and the Pope's representative in Ireland, Archbishop Charles Brown, both signalled their hope that an announcement would be made soon. Archbishop Eamon Martin said that he was expecting an answer to his invitation "very, very soon".

Speaking in Knock at the National Eucharistic Congress, the Archbishop said: "We have urged him to come and we're hoping that he will answer us very, very soon."

The Papal Nuncio, Archbishop Dr Brown, also said: "It is my fervent hope that the possibility of the Pope visiting Ireland will be realised."

He referred to Taoiseach Enda Kenny's invitation to Pope Francis in April 2013, when he said if the Irish bishops invited the Pontiff, the Irish government would support their request.

In 2014, Belfast City Council passed a motion inviting the Pope to the city.